A physicochemical process for refining metal surfaces is described and claimed in Michaud et al U.S. Pat. No. 4,491,500, issued Jan. 1, 1985, which process involves the development, physical removal and continuous repair of a relatively soft coating on the surface. The mechanical action required is preferably generated in a vibratory mass finishing apparatus, and very smooth and level surfaces are ultimately produced in relatively brief periods of time.
Zobbi et al U.S. Pat. No. 4,705,594, issued Nov. 10, 1987, provides a composition for use in the physicochemical mass finishing of metal surfaces of objects. The composition includes oxalic acid, sodium nitrate, and hydrogen peroxide, so formulated as to rapidly produce highly refined surfaces.
Michaud U.S. Pat. No. 4,818,333, issued Apr. 4, 1989, provides a physicochemical process for refining relatively rough metal surfaces to a condition of high smoothness and brightness, which is characterized by the use of a non-abrasive, high-density burnishing media.
In U.S. Pat. No. 4,906,327, issued Mar. 6, 1990, Michaud et al provide a method and composition for the physicochemical refinement of magnetic stainless steel objects.
Although the processes and chemical compositions of the foregoing inventions are most effective and satisfactory for their intended purposes, as far as is known there has not heretofore been provided a physicochemical process that is adapted for the refinement of surfaces constituted of titanium, nickel, or alloys of those metals, nor has there been provided a composition for use in such a process.
The prior art discloses a wide variety of compositions for treating titanium and/or nickel surfaces for various purposes. For example, Lipinski U.S. Pat. No. 2,881,106 discloses a method for increasing the bondability of organic polymeric materials to titanium surfaces, by treatment of the latter with an acidic (pH 3 or lower) solution containing sulfamic acid and fluoride ion. The sulfamic acid may be employed in a concentration of about 1-40 weight percent, although from a practical standpoint the upper limit appears to be 20 percent; the concentration of fluoride ion employed is 0.1 to 10, and preferably not more than 5 weight percent, and the sulfamic acid and fluoride compound are present in a weight ratio of 5 to 100:1. Treatment with the solution is said to remove the inherent oxide layer, to etch the titanium surface, and produce a film that causes the etching action to cease, the film being characterized as the reaction product of sulfamic acid and titanium.
Mahoon et al U.S. Pat. No. 4,394,224 teaches the use of sodium hydroxide/hydrogen peroxide mixtures to etch titanium surfaces and to produce an oxide layer thereupon. Activity of the composition can be enhanced by use of a catalyst, or by electrolytic techniques.
Otto U.S. Pat. No. 2,856,275 provides compositions for pickling titanium and its alloys, augmented with hydrogen peroxide or other oxidizing agent; the basic pickling solution will typically consist of a mixture of nitric and hydrofluoric acids. Use of the formulation is said to produce a clean, brilliant surface, free from any oxide film.
Akagi et al U.S. Pat. No. 4,101,440 discloses compositions containing sulfamic acid and hydrogen peroxide for effecting the release of photoresist films.
In accordance with Miller et al U.S. Pat. No. 2,864,732, a solution of a halide (e.g., fluoride), and alkali or alkaline earth metal, and an anion (e.g., phosphate, borate, oxalate, citrate, and tartrate) is used to produce a coating upon a titanium surface. Moji et al U.S. Pat. No. 3,989,876 is similar, but expressly teaches applicability to nickel and its alloys, as well. Other United States patents that generally disclose the presence of fluorides in compositions for treating titanium surfaces include Kessler U.S. Pat. Nos. 4,023,986, Villian 4,075,040 and Nakagawa et al 4,846,897.
Despite such teachings of the prior art, a demand remains for compositions, aqueous solutions, and methods that are effective for use in the physicochemical refinement of titanium and/or nickel surfaces.
Accordingly, the broad objects of the present invention are to provide novel compositions, and novel aqueous solutions which may be made from them, which solutions are effective for the physicochemical refinement of metal-surfaced objects, and particularly those having surfaces constituted of titanium or nickel (by use of which terms it is intended to encompass alloys consisting predominantly of one of those metals), by the mass finishing thereof.
A related object is to provide novel mass finishing processes utilizing such solutions, or other solutions that are capable of converting such metals to substantially pure oxide forms under normal vibratory mass finishing conditions.
Related objects of the invention are to provide such compositions, solutions and processes, by which physicochemical surface refinement is achieved at high rates of speed, with highly uniform metal removal, and without significant pitting, etching, corrosion, intergranular attack, or hydrogen embrittlement of the workpiece surfaces; and to provide such compositions, solutions and processes which are used and carried out with particular effectiveness in open, vibratory mass finishing equipment.